1. Field of the Invention
The invention relates to an apparatus for liquid treatment of disc-shaped articles, and to a heating system for use in such an apparatus.
2. Description of Related Art
Liquid treatment includes both wet etching and wet cleaning, wherein the surface area of a wafer to be treated is wetted with a treatment liquid and a layer of the wafer is thereby removed or impurities are thereby carried off. A device for liquid treatment is described in U.S. Pat. No. 4,903,717. In this device the distribution of the liquid may be assisted by the rotational motion imparted to the wafer.
Techniques for processing a surface of a disc-shaped article are typically used in the semiconductor industry on silicon wafers, for example of 300 mm or 450 mm diameter. However, such techniques may be applied for other plate-like articles such as compact discs, photo masks, reticles, magnetic discs or flat panel displays. When used in semiconductor industry they may also be applied for glass substrates (e.g. in silicon-on-insulator processes), III-V substrates (e.g. GaAs) or any other substrate or carrier used for producing integrated circuits.
When using heated process liquids, there is a problem in achieving temperature uniformity across the surface of the wafer, and the need to address that problem becomes more acute as wafer diameters increase.
In particular, as the wafer diameter increases, so too will the temperature differential between a liquid at the point where it is applied in a central region of the wafer and the same liquid after it has travelled radially outwardly to the periphery of the wafer. This results in varied etch rates as a function of the distance from the center of the wafer, and hence poor process uniformity.
Conventional approaches to alleviate this problem have included dispensing process liquid from movable arms, so-called “boom swing” dispensers; however, this involves an increase in the cost and complexity of the device as well as its operation. The problem can be addressed to some extent by increasing the flow of process liquid, and/or by dispensing a high temperature liquid such as deionized water on the opposite side of the wafer; however, these techniques result in higher consumption of process liquids.
Commonly-owned co-pending application U.S Patent Application Pub. No. 2013/0061873 describes improved apparatus equipped with an infrared heater for heating a wafer to enhance process uniformity. Although the devices of that patent application represent an improvement over conventional techniques, there remains a need to provide further enhanced process uniformity and control.